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Benefits of Breastfeeding: The Development of the Baby gut Microbiome

By Dr. Kate Dudek

The human microbiome refers to the population of microorganisms that colonise the body, working in synergy with the cells to support normal health and development. The community of microbes is vast; there are believed to be over 100 trillion variants, including bacteria, viruses, fungi, protozoa and parasites. As such, the development of the human microbiome is a highly complex process that takes approximately 3 years. As a dynamic system, the microbiome is constantly changing in response to external stimuli and internal requirements; however, the most dramatic changes occur during infancy and early childhood as the microbiome is becoming established. This is known as the 'critical window' of development and can have a substantial impact on health later in life.   

The Gut Microbiome
Microbes are present in the skin, the oral cavity and within the urogenital tract. However, the gut is the site at which they are most abundant and diverse. There is a high degree of interindividual variation, however, an effective microbiome environment will be protective, metabolic and trophic. Increased diversity correlates with enhanced protection, as the microbiomes provide a barrier against the proliferation of pathogenic organisms (i.e. those that are capable of causing disease in their host). The gut microbiome is also involved in the metabolism and digestion of food, as well as maintaining the local and systemic immune system. The gut microbiome is involved in the bidirectional communication between the CNS and the gastrointestinal system; this is known as the brain-gut axis.

In newborns, the gut microbiome plays a critical role in brain development, influencing cognitive ability and possibly contributing to mood disorders later in life. Furthermore, a well developed gut microbiome provides essential vitamins, such as vitamin K2, which is important for bone and heart health. This demonstrates how important the gut microbiome is for maintaining multi-system health benefits across the whole body.
 
Inadequate colonisation of the gut causes a microbial imbalance (dysbiosis), which makes the gut more susceptible to faulty immune responses.

What Influences the gut Microbiome of a Baby?
The gut microbiome of a newborn is less diverse than an adult; the first three years of life are critical for complete colonisation. Many factors contribute to this colonisation, including maternal factors, such as stress, infection and obesity during pregnancy. However, the major factors that contribute to the newborn microbiome structure are mode of delivery, antibiotic exposure and feeding patterns.

Mode of delivery refers to whether the baby is delivered vaginally or via Caesarean section (C-section). Babies delivered vaginally receive vertical transmission of the mother's vaginal microbes as the baby passes through the birth canal. In contrast, babies delivered via C-section receive horizontal transmission of bacteria, predominantly from the surface of the mother's skin. The vertically transmitted microbes are generally considered to be more health protective and diverse, when compared to those transmitted horizontally. Which suggests that, all being well, a natural birth is preferred over a C-section for development of an optimal microbiome in the newborn. Obviously, this is not always possible and there are cases when surgical intervention is unavoidable.

Antibiotic exposure can refer to in utero exposure, if the mother takes antibiotics whilst pregnant, or postnatal exposure, if the baby is prescribed them within the first few weeks of life. Antibiotics reduce the diversity of the gut flora, causing a microbial imbalance. There is the suggestion that probiotic supplementation my counteract some of this imbalance.

The Benefits of Breast Milk
The diet of a newborn is considered by many to be the predominant factor that influences the gut microbiome. The type of microbes found in the guts of newborns vary significantly depending on whether they are breastfed or formula fed. In general, clostridium numbers are lower in breastfed infants. Clostridium is a bacteria with over 100 species, including clostridium difficile and E.coli; it can be pathogenic in nature, causing gastrointestinal issues. Infants who were exclusively fed formula, were found to have higher levels of clostridium difficile and E.coli, than breastfed infants, which seems to have health implications for later in life. For example, higher levels of clostridium difficile and E.coli in the microbiome of a newborn, correlates with an increased risk of developing eczema, allergies and atopic dermatitis as the baby grows. Breastfeeding has also been shown to promote the proliferation of beneficial bacteria.

Gut colonisation during the first six months of an infant's life has a substantial impact on their future health status. This is one reason why the World Health Organisation encourages all mothers to exclusively breastfeed for the first six months.

Breast milk contains between 100 and 10,000 viable bacteria per milliliter and these change over time as the infant's requirements alter, so that as the baby's microbiome evolves, the microbes present in the breast milk change accordingly. Colostrum, which provides the baby with all the necessary nutrients in the first few days of life, has a more diverse microbiota than mature milk.

The differences in the microbiota composition of breastmilk and formula milk are fairly extensive. Breast milk is rich in Human Milk Oligosaccharides (HMOs), which are a type of sugar that is absent from most formula milk. HMOs are considered to be one of the major factors that contribute to the differing gut microbial environments in breastfed infants compared to formula fed infants.  HMOs exhibit prebiotic activity in the gut, potentially enhancing the development of the immune response. They also act as selective antimicrobials, preventing the proliferation of certain bacteria, but favouring other beneficial bacteria.

With weaning and, more importantly, cessation of breastfeeding comes maturation of the gut microbiome. If colonisation has been inadequate up to this point, the risk of health problems as the child grows and enters adulthood is increased. One simple way to increase the likelihood of complete colonisation is to breastfeed; this is particularly important for those mothers who have had to undergo a C-section, as their baby’s gut microbiome may already be slightly compromised. 

Sources:

  • Amon, P, and I Sanderson. “What Is the Microbiome?” Archives of Disease in Childhood - Education and Practice, vol. 102, 2017, pp. 257–260., dx.doi.org/10.1136/archdischild-2016-311643.
  • Bäckhed, F, et al. “Dynamics and Stabilization of the Human Gut Microbiome during the First Year of Life.” Cell Host & Microbe, vol. 17, no. 5, 13 May 2015, pp. 690–703., doi:10.1016/j.chom.2015.04.004.
  • Stewart, C J, et al. “Temporal Development of the Gut Microbiome in Early Childhood from the TEDDY Study.” Nature, vol. 562, no. 7728, Oct. 2018, pp. 583–588., doi:10.1038/s41586-018-0617-x.
  • Van den Elsen, L W J, et al. “Shaping the Gut Microbiota by Breastfeeding: The Gateway to Allergy Prevention?” Frontiers in Pediatrics, vol. 7, no. 47, 27 Feb. 2019, doi:10.3389/fped.2019.00047.
  • Yang, I, et al. “The Infant Microbiome: Implications for Infant Health and Neurocognitive Development.” Nursing Research, vol. 65, no. 1, 2016, pp. 76–88., doi:10.1097/NNR.0000000000000133.   
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